1. Field
One or more aspects of embodiments according to the present invention relate to image processing and more particularly to contrast enhancement in video produced by infrared (IR) detectors.
2. Description of Related Art
Infrared imaging systems, and especially systems with high-definition (HD) mid-wavelength infrared (MWIR) detectors and slow optics, may have narrow dynamic ranges, resulting in images that if displayed directly to a human viewer will appear to contain only barely distinguishable shades of grey. Moreover, an image with a single hot spot target in the field of view (FOV) may result in a gain decrease to avoid saturation at the hot spot, which may in turn result in reduced contrast over the remainder of the image. Another example of a scene that may result in a poor quality image in a short wavelength infrared (SWIR) system is a scene containing lights and a black background. In this situation also, the overall gain may be reduced to avoid saturation at the lights, resulting in poor contrast in the surrounding areas.
Contrast enhancement stages, using, e.g., a piecewise linear transform (PLT), may be used to generate images that have a greater range of brightness values, or “intensity” values, and are more useful to the viewer. In a piecewise-linear-transform, however, if two adjacent segments have a large gain differential, small changes in the scene, or noise, may cause an input pixel to be mapped alternately to one or the other of the two adjacent segments, causing unacceptable flicker in the output image. This tendency to produce flicker may be reduced by implementing a segment-to-segment (STS) gain limit for all except the end segments, but this approach limits dynamic range at the output of the contrast enhancement stage, thereby limiting the contrast enhancement available.
Thus, there is a need for a system and method for contrast enhancement, which provides significant contrast enhancement without introducing unacceptable image flicker.